A few, but increasingly important, petroleum crude feedstocks contain levels of metals such as iron and calcium which render them difficult, if not impossible, to process using conventional refining techniques. For example, calcium contaminants causing particular problems can take the form of non-porphyrin, organometallically-bound compounds. One class of these calcium-containing compounds include calcium naphthenates and their homologous series. These organo-calcium compounds are not separated from the feedstock by normal desalting processes, and in a conventional refining technique they can cause coker furnace fouling, drive residual fuel off specification for metals and result in the very rapid deactivation of hydroprocessing catalysts. One example of feedstocks demonstrating objectionably high levels of calcium compounds are West African Doba crudes.
The use of hydroxycarboxylic acids to aid in the removal of metals including calcium and iron from crude oil in refinery desalting processes is disclosed in U.S. Pat. Nos. 4,778,589 and 4,789,463, respectively.
A method of removing metals from crude oil in refinery desalting processes, in which a variety of acids, including C2-C4 hydroxycarboxylic acid are added to wash water prior to contacting the wash water with crude oil is disclosed in U.S. Pat. No. 7,497,943.
A method of removing iron from crude oil in refinery desalting processes where various chelants are added to the crude oil prior to addition of wash water is disclosed in U.S. Pat. No. 5,080,779.